This invention relates to a process and apparatus for the treatment of crude oils and, more particularly, to the hydroconversion of heavy hydrocarbons in the presence of additives and catalysts to provide useable products and further prepare feedstock for refining conversion units such as FCC or hydrocracking.
Hydroconversion processes for the conversion of heavy hydrocarbon oils to light and intermediate naphthas of good quality and for reforming feedstocks, fuel oil and gas oil are well known. These heavy hydrocarbon oils can be such materials as petroleum crude oil, atmospheric tower bottoms products, vacuum tower bottoms products, heavy cycle oils, shale oils, coal-derived liquids, crude oil residuum, topped crude oils and the heavy bituminous oils produced from oil sands. Of particular interest are the oils produced from oil sands and which contain wide boiling range materials from naphthas through kerosene, gas oil, pitch, etc., and which contain a large portion of material boiling above 538° C. (1000° F.).
As the reserves of conventional crude oils decline, these heavy oils must be upgraded to meet demands. In this upgrading, the heavier materials are converted to lighter fractions and most of the sulfur, nitrogen and metals must be removed. Crude oil is typically first processed in an atmospheric crude distillation tower to provide fuel products including naphtha, kerosene and diesel. The atmospheric crude distillation tower bottoms stream is typically taken to a vacuum distillation tower to obtain vacuum gas oil (VGO) that can be feedstock for an FCC unit or other uses. VGO typically boils in a range between at or about 300° C. (572° F.) and at or about 538° C. (1000° F.). The bottoms of the vacuum tower typically comprises at least about 9 wt-% hydrogen and a density of less than about 1.05 g/cc on an ash-free basis excluding inorganics. The vacuum bottoms are usually processed in a primary upgrading unit before being sent further to a refinery to be processed into useable products. Primary upgrading units known in the art include, but are not restricted to, coking processes, such as delayed or fluidized coking, and hydrogen-addition processes such as ebullated bed or slurry hydrocracking (SHC). All of these primary upgrading technologies such as delayed coking, ebullated bed hydrocracking and slurry hydrocracking enable conversion of crude oil vacuum bottoms to VGO boiling in the range between approximately 343 and 538° C. (650-1000° F.) at atmospheric equivalent conditions.
At the preferred conversion level of 80-95 wt-% of materials boiling above 524° C. (975° F.) converting to material boiling at or below 524° C. (975° F.), SHC produces a pitch byproduct at a yield of approximately 5-20 wt-% on an ash-free basis. By definition, pitch is the hydrocarbon material boiling above 538° C. (1000° F.) atmospheric equivalent as determined by any standard gas chromatographic simulated distillation method such as ASTM D2887, D6352 or D7169, all of which are used by the petroleum industry. These definitions of “conversion” and “pitch” narrow the range of converted products relative to pitch conversion. The pitch byproduct is solid at room temperature and has minimum pumping temperatures in excess of 250° C., which make it impractical to move over any great distance, since the pipeline would need to be jacketed with hot oil or electrically heated. It also contains inorganic solid material, which can settle out. Hence, tank storage requires stirring or circulation to prevent settling, an additional capital and operating expense.
Cohesion in solids will take place when heated into the softening region. The onset of sticking, or softening point, is difficult to determine and may require time-consuming empirical tests, for example by consolidating the solids under the expected load in a silo, followed by measuring the shear force required to move the solids. Such standard tests include ASTM D6773, using the Schulz ring-shear tester, and ASTM D6128, using the Jenike ring-shear tester. Pitch is not a pure compound and melts over a wide range. Therefore, Differential Scanning Calorimetry (DSC) will not pick up a definite melting peak that can be used as a rapid instrumental procedure.
The softening point of pitches has traditionally been measured using the Ring and Ball Softening Point Method, ASTM D36, or Mettler Softening Point Method, ASTM D3104. Both of these methods are useful for determining the temperature at which the material will begin liquid flow. This can be used, among other things, to set the minimum temperature for pitch as a liquid in the preparation of asphalt binder for paving, roofing and other and industrial uses. However, this information tells nothing about the onset of softness and cannot be directly used to determine at what point the solid will undergo plastic deformation, or start to stick together.
Solidification of pitch can be accompanied by dust generation because pitch with a higher onset of softening point can become brittle. However, pitch with lower onset of softening point can become sticky which makes handling in bulk difficult.
Better methods for processing pitch produced from SHC are needed to provide pitch that is more easily managed. Additionally, better methods are needed for assessing how easily pitch can be managed.